Alcohols are industrially a very important compound as raw materials for chemicals and pharmaceuticals, solvents and fuels. As a method of producing an alcohol, for butanol, for example, a method by synthesis from acetaldehyde by the Wacker process, and a method by industrial production from propylene, carbon monoxide and water by the Reppe process are utilized. As other examples, for 1,4-butanediol, a production method by reacting acetylene with formaldehyde, followed by hydrogenation, and a production method by reacting butadiene with acetic acid in the presence of a palladium catalyst, followed by reduction and hydrolysis are well-known. Besides those chemical synthesis methods, the conversion into a production method derived from biomass such as a fermentation process, is expected in recent years due to the decrease and price rise of oil resources, and a technique of producing a non-petroleum-derived alcohol in high purity and at low cost is required.
As a purification method of an alcohol, solvent extraction and distillation are generally known. In the solvent extraction, when the object is a lower alcohol, it is difficult to distribute it into an organic phase due to high water solubility. Therefore, specific extraction solvent and multistage extraction are required, and this leads to the problem of the increase of costs (Japanese Translated PCT Patent Application Laid-open No. 2007-525508). Furthermore, it is known that an alcohol produced by a fermentation process contains sugars as a nutrient source for microorganisms, and sugar alcohol, organic acids, inorganic salts, proteins and the like as metabolites, and that coloring impurities are generated as a by-product, by heating. For this reason, when an alcohol is purified with distillation, there are problems in the decrease of distillation yield by those impurities and the deterioration of quality due to the contamination of the coloring impurities into the purified alcohol. Furthermore, JP 2010-150248 A and JP 2010-143888 A disclose a method of separating diol, triol or butanol from sugars by a nanofiltration membrane, but there still remains a problem regarding their recovery. For this reason, a technique of efficiently recovering high quality alcohol while reducing impurities such as sugar and sugar alcohol contained in an alcohol solution is required.
It could therefore be helpful to provide a method of producing high quality alcohol by reducing sugar or sugar alcohol conveniently and efficiently in separating an alcohol from an alcohol solution which contains sugar and/or sugar alcohol as impurities.